title: Functional and structural characterisation of a viral cytochrome b5.
abstract: Cytochrome b5 is a ubiquitous electron transport protein. The sequenced viral OtV-2 genome, which infects Ostreococcus tauri, was predicted to encode a putative cytochrome b5 enzyme. Using purified OtV-2 cytochrome b5 we confirm this protein has identical spectral properties to purified human cytochrome b5 and additionally that the viral enzyme can substitute for yeast cytochrome b5 in yeast cytochrome P450 51 mediated sterol 14α-demethylation. The crystal structure of the OtV-2 cytochrome b5 enzyme reveals a single domain, comprising four β sheets, four α helices and a haem moiety, which is similar to that found in larger eukaryotic cytochrome proteins. As a product of a horizontal gene transfer event involving a subdomain of the host fumarate reductase-like protein, OtV-2 cytochrome b5 appears to have diverged in function and is likely to have evolved an entirely new role for the virus during infection. Indeed, lacking a hydrophobic C-terminal anchor, OtV-2 encodes the first cytosolic cytochrome b5 characterised. The lack of requirement for membrane attachment (in contrast to all other microsomal cytochrome b5s) may be a reflection of the small size of the host cell, further emphasizes the unique nature of this virus gene product and draws attention to the potential importance of cytochrome b5 metabolic activity at the extremes of cellular scale.
authors.affiliation: Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, UK; Biosciences, College of Life and Environmental Sciences, University of Exeter, Stocker Road, Exeter EX4 4QD, UK.
authors.forename: Emma L
authors.initials: EL
authors.lastname: Reid
authors.forename: Karen D
authors.initials: KD
authors.lastname: Weynberg
authors.forename: John
authors.initials: J
authors.lastname: Love
authors.forename: Michail N
authors.initials: MN
authors.lastname: Isupov
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Littlechild
authors.forename: William H
authors.initials: WH
authors.lastname: Wilson
authors.forename: Steven L
authors.initials: SL
authors.lastname: Kelly
authors.forename: David C
authors.initials: DC
authors.lastname: Lamb
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Allen
mesh_terms: D000595:Amino Acid Sequence; D000460:Chlorophyta / Q000821:virology; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D015786:Cytochromes b5 / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010942:Plant Viruses; D017434:Protein Structure, Tertiary; D013499:Surface Properties; D014764:Viral Proteins / Q000737:chemistry*
chemical_list: D014764:Viral Proteins; D015786:Cytochromes b5
keywords: Crystallography; Cytochrome b5; Ostreococcus tauri; P450 catalysis; Virus